Aerodynamic smoke tunnel



Nov; 4, 1952 c. L. BENEDUM 2,616,

- AERODYNAMIC SMOKE TUNNEL Filed Aug. 11, 1947 INVENTOR. Charles Leslie EIBI'LEdu'm.

ATTORNEY.

Patented Nov. 4, 1952 UNITED STATES PATENT OFFICE (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 3 Claims.

This invention relates to improvements in visual flow smoke tunnels for aerodynamic model study.

An important object of the invention is to provide an improved baffle for a smoke'tunnel of the type illustrated and described in a book entitled Der Nebelkanal by Ernst Roller, Berlin-Tempelhof, 1943, pages 38-45.

Another object is the provision of a valve in the smoke exhaust pipe of a smoke tunnel of the above-identified type for controlling the flow pattern at the trailing end of the model being studied.

Other objects and advantages of the invention will become apparent during the course of the following detailed description, taken in connection with the accompanying drawing, forming a part of this specification, and in which drawing,

Figure 1 is a front elevational view of the improved smoke tunnel.

Figure 2 is a horizontal sectional View of the tunnel substantially on the line 2-2 of Figure 1.

Figure 3 is a vertical transverse sectional view substantially on the line 3-3 of Figure 1.

Figure 4 is a diagrammatic View of the flow pattern around a model;

In the drawing, which for the purpose of illustration shows only a preferred embodiment of the invention, and wherein similar reference characters denote corresponding parts through- 2.

out the views, the numeral I5 generally designates the improved smoke tunnel including upper and lower horizontal walls I6, I! and closely spaced vertical walls l8, I9 defining an elongate duct of narrow rectangular shape in cross section. The lower wall I! is supported on longitudinal base boards 2 I, 22. The duct 29 includes a transversely enlarged air intake end portion 23, a smoke and air discharge end portion 24 provided with a circular outlet port 25 extending laterally through the rear vertical wall 19 of the duct, and a flow demonstration portion 26 intermediate the intake and discharge end portions. The vertical front Wall [8 is formed of transparent material such as glass so that-smoke flow paths along the duct may be observed.

Connected to the outlet port 25 is a suction fan fan 21 for drawing external air into the intake end portion 23 and through the flow demonstration portion 25. The speed of the fan may be varied by adjustment of a control knob 26. Air entering the intake end passes through double screens 29, 30 in a frame 3i. This frame is supported on hinges 32, 33 and releasably fastened against swinging as by hooks 34, 35. The suction fan 21 is provided with a suitable exhaust pipe 36 which should lead to a chimney or outside in the shortest possible way.

Secured to the discharge end of the tunnel is a bracket 3'! carrying an asbestos plate 38 on which the smoke generator 39 is mounted. EX- tending from the exhaust pipe 36 is a tubular line 40 leading into a cylindrical glass smoke chamber 4|. The flanged base and cover plates 42, 43 are rigidly held together and secured to the bracket by vertical anchor bolts 44 and wing nuts 45. Mounted on the cover plate 43 is a smoke oil reservoir 46 provided with an oil feed tube 41 through which kerosene or other suitable smoke oil is fed under control of a valve 48 to the flanged exterior surfaces 49 of an enclosed electric heating element 50. Energization of the heating element is controlled by a switch 5|. Volatile fuels such as gasoline must not be used and the temperature of the heating element should remain below the kindling point of the smoke oil. The cover plate 43 is provided with a gravity-seated disc 52 constituting a safety valve. Carbon deposits which form slowly on the heating element and base plate 42 may be scraped or brushed off.

Extending upwardly from the chamber 4! is a smoke pipe 53 leading over the top of the tunnel and terminating in a section 54 extending vertically downwardly through the air intake end portion. Fastened on this pipe section 64 is a vertical row of nozzles 55 for directing smoke in parallel filamentous streams toward the flow demonstration portion 26. This pipe section 54 is supported at its lower end on a threaded stem 56 for rotation and vertical adjustment, as by a circular nut 51 mounted for turning in a transverse bar 58. The orientation of the nozzles 55 in the air intake section may be changed by swinging handle lever 59. A butterfly valve 66 is provided for controlling the flow of smoke through the pipe 53.

Mounted for rotation in a bearing 6i extending through the rear wall I9 is a hollow sleeve 62 carrying pins 63, 64 adapted for engagement with special models (not shown) having adjustable control surfaces. Rotatable in the hollow sleeve is a shaft 65 supporting a model 66 in the flow demonstration portion. Extending through the base of the tunnel is a hollow shaft 6'! rotatable by a knob 66 and adapted to transmit rotary motion to the hollow sleeve 62, as by pulleys 68, 69 and belt 10. Extending through the hollow shaft 61 is a shaft ll rotatable by a knob 12 and adapted to transmit rotary motion to the shaft 65 as by pulleys T3, 14 and belt 15. The rear wall I9 is provided with a hinged section 16 which may be swung open to permit changing models. The rear wall l9 of the tunnel may be coated with black material such as paint or fabric, so that the bright, white wisps of smoke produced by the generator using kerosene will stand out even more prominently. Mounted respectively above and below the upper and lower walls l6, I! are tubular electric lamps TI, 18 which illuminate the flow demonstration portion 26 through slots 19, 80 so that the tunnel may be operated in a dark room. The suction fan 21 and lamps 1,1, 18 may be energized through a single switch Bl In order to prevent converging of the smoke filaments at the circular outlet port 25, I provide, in the path of travel of the air and smoke, a V-shaped bafile 82 extending across the narrow dimension of the duct and havingitsdivergent trailing end portions 83, 84 terminating a little forwardly of the outlet port 25. This bafile 82 tends to make the smoke coming from the nozzles 55 flow through the demonstration portion in substantially parallel lines except in zones where a flow pattern is formed by the presence of a model.

I also provide a butterfly valve 85 in the exhaust pipe 36 beyond the point ofconnection of the tubular line '40 for controlling the 110w pattern at the trailing end of a model in the damonstration portion. A guide vane assembly 86 may be inserted in the fiow demonstration portion to reduce the size of the duct'for special tests.

In the operation of the tunnel, the heating element of the smoke generator is'energized for a warming-up period by closing switch 5!, and the oil valve 48, is adjusted so that drops fall at suitably spaced intervals for the production of the quantity of smoke desired. The contents of the smoke chamber 41 constitute a pneumatic cushion between the suction fan and the nozzles. By proper adjustment of the butterfly valve 85, wisps of smoke may be caused to curl in the area at the trailing end of a model such as diagrammatically shown in Figure 4. This diagram ilelustrates a tw0-dimensional fiow pattern, that is, the model extends across the field of fiow from the back of the tunnel to the glass front panel. Three-dimensional flow about a monoplane wing can be demonstrated with the arrangement shown in Figure 1. Here a wing model is set at a small angle of attack with the span crosswise of the smoke filaments 81. The smokenozzles 55 may be moved so that the filaments pass either above or below the-model, or directly over it. With the filaments correctly positioned, the wingtip vortices will be clearly exhibited, as shown in Figure 1.

Various changes may be made in the form of invention herein shown and described without departing from the spirit of the invention or the scope of the .following claims.

The invention described herein maybe manufactured and used by or for the Goy ernment of the United-States of America-for governmental purposes without the payment of any royalties thereon or therefor.

.of-spaced smoke discharge nozzles in the intake end portion, means supplying smoke to the nozzles, a smoke and air discharge end portion having a sidewall provided with a substantially circular outlet port extending laterally from a zone located substantially on the longitudinal axis of the duct, a flow demonstration portion intermediate said end portions, a suction fan communicating with the outlet port "for withdrawing air and smoke from the discharge end portion, said outlet end portion being provided with a V-shaped baflie extending across the narrow dimension of the duct and disposed in the path of travel of the smOke. and air forwardly of the outlet port, said bafiie including divergent trailing end portions terminating near opposite sides of the outlet port.

' 2. A smoke tunnel of the type having an elongate duct of narrow rectangular shape in cross section including an air intake end portion, a row of spaced smoke discharge nozzles in the intake endportion, means supplying smoke to the nozzles including a smoke generating chamber, asmoke and air discharge end portion provided with an outlet port, a. flow demonstration portion intermediate said end portions, means for supporting a model in the demonstration portion, a suction fan communicating with the-outlet port for withdrawing air and smoke from the discharge endportion, an exhaust pipe connected to the suction fan for carrying away said air and smoke, said outlet end portion being provided with a V-shaped baffle disposed symmetrically with respect to the longitudinal center line of said duct with the apex of the V pointed upstream in the path of travel of the smoke and air forwardly of the outlet port, means providing a passageway between the exhaust pipe and the smoke generating chamber for supplying smoky air thereto, and a valve in the exhaust pipe for creating pressure changes in the tunnel and thereby controlling the flow pattern at the trailing-end of the model.

3. In a smoke tunnel as defined in claim 1, said baffle consisting essentially of a V-shaped structure, positioned symmetrically about the longitudinal center line of said duct with the apex of the V point-ed upstream and the legs of the V being disposed substantially normal to each other.

CHARLES LESLIE BENEDUM.

REFERENCES CITED The following references are of record in the file of; this patent:

UNITED STATES PATENTS Number Name Date 1,6 6,984 Fale i? J 1 192.8 1.960.78 Frankctsl. ay 2 1 34 .2,13;1, 890 .Realon. g Nov. 1, 1938 2,164,000 ,Ke11er June 27, 1939 2,254,680 Harvey 9-..- Sept. 2, 1941 2,401,761 Holtham June 11, 1946 FOREIGN PATENTS Number Country Date 506,159 Great Britain May 24, 1938 OTHER REFERENCES stelle fiir Luitfahrts und Seetechnick, Berlin- Tempelhof; pages 27-46. 

